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<script>
	//参数个数，可以不一样多
	function fun(a, b, c){	
		console.log(b); //b =>undefined
		console.log(a+b+c);
	};
	
	//调用
	fun(3); //什么情况会是NaN?  只要和undefined参与运算就会是NaN
	//如果传入多个实参，那么运行的时候只会按照形参对应的来接收
	fun(3, 5, 7, 8)
</script>
